1. Field of the Invention
The invention relates to a system for recording and reproducing picture signals comprising a phase-modulated or frequency-modulated picture color signal on and from a magnetic tape in adjacent tracks which are inclined relative to the longitudinal direction of the tape, the picture signals being recorded and reproduced in a first recording mode and in a first reproduction mode with a first tape speed, and in a second recording mode and in a second reproduction mode with a second tape speed which is preferably a sub-multiple of the first tape speed, the video signals recorded in the first recording mode being additionally reproducible in at least one first further reproduction mode with at least one first further tape speed which differs from the first tape speed, and the video signals recorded in the second recording mode being additionally reproducible in at least one second further reproduction mode with at least one second further tape speed which differs from the second tape speed, modulated character signals, which comprise a phase-modulated or a frequency-modulated character color signal, being insertable into at least the reproduced picture signals, the system having a conversion stage for reconverting a reproduced picture color signal to an original frequency range, the conversion stage supplying the reconverted picture color signal to an output, having a detection stage which is arranged behind the output of the conversion stage and which, in the case of a phase-modulated picture color signal, is constructed as a phase detection stage for detecting the phase of the burst signal in the reconverted picture color signal and, in the case of a frequency-modulated picture color signal, is constructed as a frequency detection stage for detecting the frequency of the non-modulated color subcarrier signals in the reconverted picture color signal, the detection stage supplying a detection signal of half the line frequency to an output, having a first switching device arranged behind the output of the conversion stage and controllable by means of a control device, the first switching device being set to a first switch position by the control device in the second further reproduction mode of the system, in which first switch position, a first delay device of the system with a delay time of one line period is arranged in series with the first switching device and the reconverted picture color signal supplied to the output of the conversion stage is transferred with a delay of one line period to a further signal-processing stage of the system, the first switching device being set to a second switch position by the control device in all the other reproduction modes of the system, in which second switch position, the first delay device is bypassed and the reconverted picture color signal supplied to the output of the conversion stage is transferred without a delay to the further signal-processing stage, and having a character generator for the generation of non-modulated character signals and a modulator which is connected to the character generator and which enables the non-modulated character signals to be converted into modulated character signals to be inserted, and having a character insertion stage which is connected to the further signal processing stage and to the modulator and which is adapted to insert the modulated character signals at least into the reproduced picture signals, the modulator comprising a control input to the a control signal of half the line frequency is applied, which control signal being phase-locked to a detection signal of half the line frequency supplied to the output of the detection stage, in order to achieve that the reproduced picture color signals and the character color signals to be inserted are locked in phase in the case of a phase-modulated picture color signal, and are locked in frequency in the case of a frequency-modulated picture color signal.
2. Description of the Related Art
A system of the type defined in the opening paragraph is known from the prior art. In such a system, character signals corresponding to colored characters, such as colored letters or colored graphic symbols, can be inserted into picture signals corresponding to color pictures. This should be effected in such a way that the colored characters corresponding to the character signals are always reproduced on the display screen of a television receiver with the same color, i.e. in such way that, for example, red characters always and in all modes appear as red characters on the display screen on which the picture signals are displayed as a colored background picture.
When picture signals and character signals are reproduced on the display screen of a television receiver, the reference for the demodulation of both the background-picture color signal and the character color signal are formed by burst signal of the background-picture color signal in the case of phase-modulated color signals, as is the case with the PAL system, and by the unmodulated color subcarrier of the background-picture color signal in the case of frequency-modulated color signals, as is the case with the SECAM system. Therefore, a color signal component of a character color signal and a color signal component of a background-picture color signal should be in the same phase relationship to the burst signal of the background-picture color signal in the case of phase-modulated color signals, and they should be in the same frequency relationship to the unmodulated color subcarrier signals of the background-picture color signal in the case of frequency-modulated color signals in order to ensure that both color signal components are reproduced in the same color on the display screen. In the case of phase-modulated color signals, an inserted character color signal should therefore be locked in phase, and in the case of frequency-modulated color signals, it should be locked in frequency to the background-picture color signal in order to guarantee that the character color signal is always reproduced on the display screen with a specified color.
In order achieve this in the prior-art system for processing picture signals with a phase-modulated picture color signal, a rectangular detection signal of half the line frequency, appearing on the output of the detection stage formed by a phase detection stage, is applied to a generator stage for the generation of a rectangular control signal of half the line frequency, the detection signal controlling this generator stage so as to provide phase-locking of the generated control signal to the detection signal. The rectangular control signal of half the line frequency thus generated is applied to the control input of the modulator. Each positive edge of this rectangular control signal corresponds to a positive phase (+45.degree.) of the burst signal of the background-picture color signal and a positive phase of the (R-Y) component of the background-picture color signal, and each negative edge corresponds to a negative phase (-45.degree.) of the burst signal of the background-picture color signal and a negative phase of the (R-Y) component of the background-picture color signal. In the modulator, the positive phase of the (R-Y) component of the character color signal is assigned to each positive edge of the rectangular control signal and the negative phase of the (R-Y) component of the character color signal is assigned to each negative edge of the rectangular control signal. In this way, it can be achieved that the phase of the (R-Y) component of the character color signal is rigidly locked to the rectangular control signal and thus to the burst signal and to the phase of the (R-Y) component of the background-picture color signal, which corresponds to the rigid phase lock between the character color signal and the background-picture color signal explained above.
In the prior-art system, the rectangular control signal is applied to the modulator independently of the reproduction mode to which the system has been set. However, if the system is set to a second further reproduction mode, in which reproduction is effected with a tape speed which differs from the low second tape speed, i.e. in the case of so-called multi-speed reproduction of a long-play recording, this results in color reproduction problems in the reproduction of inserted colored characters because in such a reproduction mode, in order to compensate for reproduction-dependent time shifts in the background-picture color signal, this color signal must be applied via a delay device having a delay of one line period, which device may be constituted by a delay line or a stage for the formation of a conjugate signal, as a result of which the rigid phase lock between the burst signal and the (R-Y) component in the background-picture color signal, on the one hand, and the rectangular control signal and consequently the (R-Y) component of the character color signal, on the other hand, will be lost. When colored character signals are inserted into picture signals to be reproduced in a so-called multi-speed reproduction mode of a long-play recording, this will result in the characters being reproduced on the display screen of a television receiver with an undesired wrong color.